As is well known, ceramic sanitaryware (such as toilet bowls, bidets, washbasins, console sinks, hand basins, wash tubs, shower trays, flush tanks and the like) is made by casting a fluid mixture (known as “slip” in the jargon of the trade, consisting of a ceramic body in aqueous suspension) in customary moulds with a porous structure, which may be divided into two or more parts.
The mould gives the article of sanitaryware the required shape and after a certain length of time (necessary to draw out a part of the water) the article is extracted from the mould in a solid form, known as “greenware” (still having a water content of between 16% and 20% by weight) and hence still subject to plastic deformation.
Contact of the sanitaryware article with the air (step of pre-drying the “greenware”) brings about two main changes in the article, the first bringing it to an intermediate “leatherhard” state (in which the initial water content is reduced by 30% to 50%) and the second, to an almost finished “whitehard” state (in which the water content is practically zero): in these two states, the sanitaryware article is no longer subject to high levels of plastic deformation.
In one or more of these three different states, the sanitaryware article usually undergoes a plurality of finishing processes such as, for example, fettling, drilling of holes, slotting, radiusing and so on.
Thus, once the ceramic products have been demoulded, that is to say, removed from the mould, whether they have been cast in porous resin moulds (at high pressure) or in gypsum moulds (at low pressure), they must be held in a secure, stable position to enable the subsequent steps in the manufacturing process, including both drying and finishing, to be completed.
The supporting systems currently used are structured in a, so to speak, “rigid” manner, that is to say, they do not adapt to the linear and weight variations of the products (causing movements with horizontal and vertical components) as the products change from one state to another, in particular from the “green” to the “leatherhard” state.
Indeed, as the product dries, its diminishing water content results in weight loss and significant shrinkage of between 2% and 4% of its original size.
Current state-of-the-art stands and auxiliary structures supporting the base and, for example, the sides of a product are basically static supports and, as such, are unable to satisfactorily adapt to the settling that the product undergoes.
That means the state of the product must be closely monitored and the supporting structure adjusted according to the changes in the product: all of this is left to, and depends on, the experience of personnel responsible for that particular stage in the manufacturing process.
Obviously, if the supporting structure is not adjusted or, when necessary, parts of it substituted, the resulting tensional and/or deformation stresses can lead to irreparable defects or even breakage of the product.
A typical example of these problems is that of a fixture known in the trade as a “one-piece” toilet, namely, a toilet bowl (that is, a pan with added rim) made as a single part with a flush tank partially protruding from the back of the pan.
This type of sanitary fixture is too unstable to be handled after being demoulded: its centre of gravity does not permit the required balanced position without additional means (props) to support the sides and back of it during post-moulding operations such as fettling, for example.
This, as mentioned above, involves constant monitoring of the production process and repositioning of the props as the product changes from one state to another. These operations take time, may interrupt finishing processes and involve high scrap rates.